A diode and resistors are arranged on the side of the input electrode relative to an input protection MOS transistor for lengthening a rise time of a voltage surge input thereto to cope with an abrupt surge of voltage by way of the time constant of the junction capacitance of the diode and the resistances of the resistors.
The output circuit is substantially identical to the i/o protection circuit for protecting the input circuit which is described above. In case of the output protection circuit, an output MOS transistor itself serves as the output protection MOS transistor. Since the output MOS transistor generally occupies a large area, the protection diode serving as a capacitor is not used.
The conventional input or output protection circuit, however, reacts as a delay element also to normal signals since it is equipped with a protection diode and protection resistors for lengthening the rise time of input voltage. As a result, the transmission of a signal in the input or output circuit is delayed so that speeding up device operation as a whole is prevented. Since miniaturization of and the speeding up of device operation is currently in progress, the above-mentioned delay is not negligible as a factor preventing the speeding up.
The present invention provides an input protection circuit or an output protection circuit which realizes the speeding up of a device operation by solving the problem relating to transmission delay of the signal by the protection diode and protection resistors set forth above.